The overall objectives of this proposal are to continue our studies on the mechanism of the immunopotentiating properties of retinol and extend these studies to include a representative synthetic retinoid, 13-cis retinoic acid which has been successfully used for epithelial tumor therapy. These objectives will be achieved by measuring antibody formation (several subclasses) and the cell-mediated response after retinoid administration. The retinoids will be administered either intraperitoneally or orally using an acute (one time) or prolonged regimen. Assessment of the effects of these retinoic compounds on individual immune cell populations will also be assessed. This will be achieved in Vivo by measuring antibody response to a T-independent antigen after treatment with the various regimens of retinoids. In addition, the effects of the retinoids on other cellular parameters will be assessed in vitro by measuring the ability of these retinoids to modify the specific blastogenic responses of B and T lymphocytes. The effect of the retinoids on macrophage populations will be measured by assaying phagocytosis, lysis, and antigen presentation. The ability of the retinoids to modify the ability of thymus epithelial cells to induce T-cell differentiation will also be assessed.